Chapter 8

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Chapter 8

Section 8.5: Translation

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Objectives

• SWBAT describe how mRNA codons are translated into amino acids.

• SWBAT summarize the process of protein synthesis.

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Vocabulary

• Translation • Codon • Stop codon• Start codon • Anticodon

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The Process of Translation

• Translation is the process that converts, or translates, an mRNA message into a polypeptide.– One or more polypeptide chains make up a

protein. • While DNA and RNA only use four nucleotides

each in their codes, the language of proteins uses 20 amino acids.

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Triplet Code

• A codon is a three-nucleotide RNA sequence that codes for an amino acid.

• The genetic code matches each codon to its amino acid or function (the start/stop codons).

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Triplet Code

Methionine is the start codon while there are three stop codons.

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Triplet Code – for Amino Acids

• A change in the order in which codons are read changes the resulting protein.

• Regardless of the organism, codons code for the same amino acid.

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Anticodon

• An anticodon is a set of three nucleotides that is complementary to an mRNA codon (a codon of CCC binds with an anticodon of GGG).

• An anticodon is carried by a tRNA.

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Ribosomes (rRNA)

• The large and small ribosomal subunits pull mRNA through the ribosome, reading it one codon at a time.

• The large subunit has three binding sites for tRNA’s anticodon.

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TranslationFor translation to begin, tRNA binds to a start codon and signals the ribosome to assemble.

A complementary tRNA molecule binds to the exposed codon, bringing its amino acid close to the first amino acid.

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Translation• The ribosome helps form a polypeptide bond between the amino

acids.• The ribosome pulls the mRNA strand the length of one codon.

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Translation• The now empty tRNA molecule exits the ribosome.

– A complementary tRNA molecule binds to the next exposed codon.

– Once the stop codon is reached, the ribosome releases the protein and disassembles.